Fax/Mail Servers

Hi I'm new here.After 15 years as a database programmer I just took a job in a small office environment in more of a CTO roll. I am looking for a Fax/ Mail server that uses a shared phone book, preferabbly Unix based as we are running an AIX server for our file server/"database server". Any recomendations or pointers would be appreciated.

Here's one place to look. ServerWatch is another site in the Jupitermedia network.
Here's a link to its Mail Server page.
http://www.serverwatch.com/stypes/index.php/TWFpbA==

Thanks, I'll chec it out